Components in the hot gas flow path of gas turbines often have internal cooling channels. Cooling effectiveness is important in order to minimize thermal stress on these components. Cooling efficiency is important in order to minimize the volume of air diverted from the compressor for cooling. Film cooling provides a film of cooling air on outer surfaces of a component via holes from internal cooling channels. Film cooling can be inefficient, because so many holes are needed that a high volume of cooling air is required. Thus, film cooling has been used selectively in combination with other techniques. Impingement cooling is a technique in which perforated baffles are spaced from a back surface of a component opposite a heated surface to create impingement jets of cooling air against the back surface. It is also known to provide serpentine cooling channels in a component.
The trailing edge portion of a gas turbine airfoil may include up to about ⅓ of the total airfoil external surface area. A trailing edge is thin for aerodynamic efficiency, so it receives heat input on its two opposed exterior surfaces that are relatively close to each other, and thus a relatively high coolant flow rate is required to maintain mechanical integrity. Trailing edge cooling channels have been configured in various ways to increase efficiency. For example U.S. Pat. No. 5,370,499 discloses a mesh of coolant exit channels in the trailing edge. Trailing edge exit channels commonly have a transverse sectional profile that is rectangular, circular, or oval.
The present invention increases heat transfer efficiency and uniformity in cooling channels such as those in the trailing edge of turbine airfoils, thus reducing the coolant flow volume needed.